Construction Of Enzyme@HOF Biological Nanoreactor And The Application In Chiral Catalytic Reactions

The development of society and the demand for human health have led to the rapid development of chiral drugs.Biological enzymes have a wide range of sources,strong specificity,and green efficiency.Therefore,using enzyme chiral pockets to obtain optically active substances is a hot topic in the field of chemical research.However,enzymes are expensive and it is difficult to recover from the reaction system for biological enzymes.In addition,the purification and separation of biological enzymes are difficult.In order to solve the problem of enzyme reusability,immobilization technology has emerged.In recent years,porous organic framework materials,such as metal organic frameworks,covalent organic frameworks,and hydrogen-bonded organic frameworks,have been widely used for enzyme immobilization due to their adjustable pore size and large specific surface area.Among them,hydrogen-bonded organic frameworks have mild synthesis conditions and biocompatibility,which can be said to have the advantages of both metal organic frameworks and covalent organic frameworks.Therefore,they are considered an ideal platform for enzyme immobilization.Based on this,we hope to form a protective shell composed of hydrogen-bonded organic frameworks on the outer surface of a bulky enzyme through in-situ self-assembly,which facilitates the separation of heterogeneous biocatalysts from the system and achieves the goal of recycling.The specific research content of this paper is as follows:(1)The fragility and reversibility of hydrogen-bonds result in the collapse of the hydrogen-bonded organic frameworks structure after vacuum activation or removal of solvent molecules.The electrostatic interaction between monomer molecules is conducive to the formation of structurally ordered and permanently porous hydrogen-bonded organic frameworks.Firstly,according to the methods reported in the literature,HOF-1 was successfully prepared using tetrahedral tetraphenylamidine salt(1-4Cl)and tetraphenylcarboxylic acid(1-COOH)in aqueous solution.Then,a benzene ring was coupled to the monomer to increase the linker.Finally,HOF-2 with high crystallinity was synthesized by changing experimental conditions such as solvent and temperature.(2)Candida antarctica lipase B can be used for kinetic resolution of racemic 1-phenylethanol to obtain esterification products of(R)-1-phenylethanol and(S)-1-phenylethanol.In view of this,we constructed two types of single enzyme nanobioreactors by immobilizing Candida antarctica lipase B into HOF-1 and HOF-2 through in situ selfassembly,respectively CALB@HOF-1 and CALB@HOF-2.The changes of materials before and after enzyme immobilization were characterized by scanning electron microscope,powder X-ray diffraction,total reflection fourier transform infrared spectroscopy,confocal laser scanning microscope and nitrogen adsorption-desorption isotherm,and the successful enzyme loading was determined.The prepared materials were applied to the resolution of racemic phenylethyl alcohol,and the esterification products with ee values of 99% and the phenylethyl alcohol with S-configuration with ee values of92% were obtained.The application of the substrates was wide,which expanded the application of hydrogen-bonded organic frameworks immobilized enzyme materials in the preparation of chiral aromatic alcohols and their derivatives.(3)The theoretical yield of the product obtained by the kinetic resolution of racemic compounds using lipase is only 50%,which does not meet the development requirements of atom economy.The theoretical yield of the conversion of prochiral ketones to chiral alcohols catalyzed by alcohol dehydrogenase can reach 100%.Therefore,we immobilized alcohol dehydrogenase and glucose dehydrogenase into hydrogen-bonded organic framework to form a dual enzyme cascade nanoreactors to catalyze the regeneration of coenzymes.They are named ADH@GDH@HOF-1 and ADH@GDH@HOF-2.The prepared material was subjected to asymmetric catalytic reaction of acetophenone in buffer solution to obtain(R)-1-phenylethanol with the yield of 99% and high enantioselectivity(ee value of 99%).The material exhibits excellent performance in repeated utilization experiments,with the yield of over 70% after five recycles.It exhibits good catalytic activity over a wide range of p H,and its enantioselectivity is not affected.Finally,the suitability of substrates was explored,and the experimental results showed that ketones with different structures could be converted into R-configuration alcohols with an ee value of 99%,which were applied to the synthesis of(S)-Rivastigmine and(R)-Fendiline.In summary,we have prepared hydrogen-bonded organic frameworks materials that are universally applicable to natural enzymes and successfully applied them to the preparation of chiral 1-phenylethanol and derivatives,providing a new idea for chemical workers in asymmetric synthesis.